1. Field of the Invention
The present invention relates to a swing member device, and an optical deflector and image-forming apparatus employing the swing member device. The present invention relates also to a technique for an optical deflector employing a swing member device, which is useful for an image-forming apparatus such as a projection display which projects an image by scanning with a deflected light beam; a laser beam printer utilizing an electrophotography process; and a digital copying machine.
2. Description of the Related Art
A microscopic mechanical member produced from a wafer by a semiconductor process can be worked in a micrometer size. Various functional elements are produced with the microscopic mechanical member. For example, various actuators (swing member device) are disclosed which utilizes a resonance phenomenon of a swingable part (swing member) produced by such a technique and is swung torsionally (see U.S. Pat. No. 7,050,211, etc.).
Such an optical deflector for scanning with a light beam by utilizing the resonance phenomenon of the swingable part (swingable member) having a mirror as the optical deflector on the swingable member is advantageous in comparison with a conventional optical scanning system employing a rotating polygon mirror as described below. That is, the optical deflector can be miniaturized; the optical deflector employing a silicon single crystal produced by a semiconductor process does not cause metal fatigue and has high durability; and the optical deflector consumes less electric power. In particular, the power consumption can be further reduced by driving the swingable member at or near the frequency of the intrinsic oscillation mode of torsional swing of the swingable member.
However, the aforementioned optical deflector employing the swing member device utilizing the resonance phenomenon has a disadvantage of irregular deviation of the swingable member during the swing motion, causing deterioration of image quality with the image formation apparatus. The irregular deviation of the swingable member is caused by an unsteady drag force caused by environment in the driving region of the swingable member driven by a driving unit. That is, the air around the plate of the swingable member is disturbed during swing motion of the swingable member by air resistance and makes the swing motion unstable. To prevent the irregular swing deviation of the swingable member, the swingable member may be sealed in a vacuum or at a low pressure. However, this makes the production process complicated and raises the production cost.
To solve the above problems, the present invention intends to provide a swing member device which has a simple constitution and can be produced at a low cost, and is affected less by unsteady drag force caused by ambient atmosphere in the region of movement of the swingable member. The present invention intends also to provide an optical deflector and an image-forming apparatus employing the above swing member device.